1. Field of the Invention
The present invention relates to a memory, and more particularly, it relates to a memory comprising memory cells including diodes.
2. Description of the Background Art
A crosspoint mask ROM (hereinafter referred to as a diode ROM) having a plurality of memory cells, each including a diode, arranged in the form of a matrix is known in general as an exemplary memory.
In a conventional diode ROM, a plurality of word lines and a plurality of bit lines are arranged to intersect with each other in a memory cell array. These word lines and bit lines are connected to a row decoder and a column decoder respectively. An address input circuit, a row decoder, a column decoder, a sense amplifier and an output circuit are provided outside the memory cell array. A plurality of memory cells each including a diode are provided in the memory cell array. The plurality of memory cells are arranged in the form of a matrix along the plurality of word lines and the plurality of bit lines respectively, while a prescribed number of such memory cells are connected to each word line through the corresponding selection transistor. Cathodes of the diodes included in the prescribed number of the memory cells connected to the corresponding word line are connected to a common conductive line. Anodes of the diodes are connected to the bit lines.
In a conventional data read operation, the row decoder first changes the potentials of the plurality of the word lines on the basis of address data output from the address input circuit. The bit line corresponding to the selected memory cell is electrically connected to the sense amplifier by the column decoder on the basis of address data output from the address input circuit. Thus, the potential of the selected bit line is determined and amplified in the sense amplifier and an output circuit thereafter outputs a signal.
Dissimilarly to the structure in which the signals of the aforementioned memory cells are read through the bit lines, source lines provided to intersect with the plurality of word lines and electrically connected to the cathodes of the diodes through selection transistors may be provided and the signals of the memory cells included in the diodes may be read through the source lines. At this time, the sense amplifier is connected to the source lines, the potentials of the source lines are determined and amplified in the sense amplifier and the output circuit thereafter outputs the signals.